1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a substrate for a liquid crystal display (LCD) device and a fabricating method thereof.
2. Discussion of the Related Art
Until recently, display devices have typically used cathode-ray tubes (CRTs). Presently, much effort is being expended to study and develop various types of flat panel displays, such as liquid crystal display (LCD) devices, plasma display panels (PDPs), field emission displays, and electro-luminescence displays (ELDs), as a substitute for CRTs. Of these flat panel displays, the LCD devices have many advantages, such as high resolution, light weight, thin profile, compact size, and low voltage power supply requirements.
In general, an LCD device includes two substrates that are spaced apart and face each other with a liquid crystal material interposed between the two substrates. The two substrates include electrodes that face each other such that a voltage applied between the electrodes induces an electric field across the liquid crystal material. Alignment of the liquid crystal molecules in the liquid crystal material changes in accordance with the intensity of the induced electric field into direction of the induced electric field, thereby changing the light transmissivity of the LCD device. Thus, the LCD device displays images by varying the intensity of the induced electric field.
FIG. 1 is a perspective view of a LCD device according to the related art. FIG. 2 is a schematic view of structures of a peripheral line on a substrate for an LCD device according to the related art.
As shown in FIG. 1, the LCD device 9 includes a first substrate 10, a second substrate 20 and a liquid crystal material 18. The second substrate 20 is referred to as a color filter substrate that includes a color filter pattern 24, a black matrix 22 between the color filter patterns 24, and a common electrode 28 on both the color filter pattern 24 and the black matrix 22. The first substrate 10 is referred to as an array substrate that includes a data line 14 and a gate line 12 that cross each other and define a pixel region P. A pixel electrode 16 and a thin film transistor T as a switching element are positioned in each pixel region P. Thin film transistors T, which are disposed adjacent to where the data lines 14 and the gate lines 12 cross, are disposed in a matrix form on the first substrate 10. A data pad electrode 15 is disposed on one end of the data line 14. Thought not shown in FIG. 1, a gate pad electrode is disposed on one end of the gate line 12.
To fabricate the related art LCD device, multiple mask processes are conducted, for example, a five-mask method or a four-mask method.
A five-mask method includes a first mask process for forming the gate line 12 and a gate electrode of the thin film transistor T, a second mask process for forming a semiconductor pattern of the thin film transistor T, a third mask process for forming the data line 14 and source and drain electrodes of the thin film transistor T, a fourth mask process for forming a passivation layer, and a fifth mask process for forming a pixel electrode 16. The first to fifth mask processes are conducted with a wet-etching, method or a dry-etching method.
When the five-mask method is used, a peripheral line 80, as shown in FIG. 2, including a common line, a ground line and so on is formed during the first to third processes. The peripheral line 80 is formed in a non-display region ND defined at peripheral portions of a display region D having the pixel regions P. The peripheral line 80 has larger area than the data line 14 such that a resistance thereof is reduced. In the five-mask method, since each layer is patterned with each corresponding mask process, the patterned layer is not affected by different mask processes. However, to decrease production process time and cost, the number of mask processes used is reduced.
The four-mask method includes four mask processes. The four-mask method includes a first mask process for forming the gate line 12 and a gate electrode, a second mask process for forming the data line 14, source and drain electrodes and a semiconductor pattern therebelow, a third mask process for forming a passivation layer, and a fourth mask process for forming the pixel electrode 16. The first to fourth mask processes are conducted with a wet-etching method or a dry-etching method.
When the four-mask method is used, the peripheral line 80 is formed during the first and second processes. The second mask process is conducted to pattern not only the data line 14 and the source and drain electrodes, but also the semiconductor pattern therebelow. In other words, the data line 14 and the source and drain electrodes, and the semiconductor pattern therebelow are patterned with the same mask process. Accordingly, etching times for the second mask process increase. Further, when the dry-etching method for the second mask process is used, the amount of etching gases used increase. Therefore, the peripheral line 80 at the same layer as the data line 14 is over-etched during the second mask process, and thus portions of the peripheral line 80 may be etched away. Further, since the peripheral line 80 has a large area to reduce the resistance thereof, plasma generated for the dry-etching method is concentrated on the peripheral line 80. Therefore, the peripheral line 80 is further over-etched, and thus portions of the peripheral line 80 may be etched away. As a result, the resistance of the peripheral line 80 is changed, and thus display quality of the LCD device is degraded.